In the field of non-impact printing, the most common types of printers have been the thermal printer and the ink jet printer. When the performance of a non-impact printer is compared with that of an impact printer, one of the problems in the non-impact machine has been the control of the printing operation. As is well-known, the impact operation depends upon the movement of impact members such as wires or the like and which are typically moved by means of an electromechanical system which may, in certain applications, enable a more precise control of the impact members.
The advent of non-impact printing as in the case of thermal printing, brought out the fact that the heating cycle must be controlled in a manner to obtain maximum repeated operations. Likewise, the control of ink jet printing in at least one form thereof, must deal with rapid starting and stopping movement of the ink fluid from a supply of the fluid. In each case, the precise control of the thermal elements and of the ink droplets is necessary to provide for both correct and high-speed printing.
In the matter of ink jet printing, it is extremely important that the control of the ink droplets be precise and accurate from the time of formation of the droplets to depositing of such droplets on paper or like record media and to make certain that a clean printed character results from the ink droplets. While the method of printing with ink droplets may be performed either in a continuous manner or in a demand pulse manner, the latter type method and operation is disclosed and is preferred in the present application as applying the features of the present invention. The drive means for the ink droplets is generally in the form of a crystal or piezoelectric type element to provide the high speed operation for ejecting the ink through the nozzle while allowing time between droplets for proper operation. The ink nozzle construction must be of a nature to permit fast and clean ejection of ink droplets from the print head.
In the ink jet printer, the print head structure may be a multiple-nozzle type with the nozzles aligned in a vertical line and supported on a print head carriage which is caused to be moved or driven in a horizontal direction for printing in line manner. The ink droplet drive elements or transducers may be positioned in a circular configuration with passageways leading to the nozzles.
Alternatively, the printer structure may include a plurality of equally-spaced horizontally aligned single nozzle print heads which are caused to be moved in back-and-forth manner to print successive lines of dots in making up the lines of characters. In this latter arrangement, the drive elements or transducers are individually supported along a line of printing.
Previous and current designs for drop-on-demand ink jet print heads are sensitive to the ingestion of air into or the presence of air in the supply of ink. Even a small air bubble can interrupt or fault the performance of transducers that expel ink droplets from a nozzle by means of pressure pulses created within an ink-filled chamber or channel.
It is proposed to provide an ink jet transducer or ink droplet drive element that operates, with the ink being in a condition under hydrostatic pressure, on the principle of an electromagnetic valve assembly for initiating and controlling the flow of ink droplets toward the record media.
Representative documentation in the field of ink jet transducers or drive elements includes U.S. Pat. No. 3,424,198, issued to A. R. Erbach on Jan. 28, 1969, which discloses a combined pressure regulating and pressure release valve having a solenoid driven carriage and a pair of balls rotatably mounted in the carriage wherein one ball always seals an orifice except while the carriage is being moved from one position to another position.
U.S. Pat. No. 4,152,710, issued to M. Matsuba et al. on May 1, 1979, discloses an ink liquid supply system having a reservoir and an electromagnetic cross valve for controlling the flow direction of the ink, and a drain tank with a ball valve functioning to absorb the rapid flow of the ink.
U.S. Pat. No. 4,183,031, issued to E. L. Kyser et al. on Jan. 8, 1980, discloses an ink supply system with a pressure sensor and a valve operated by the sensor and integrally incorporated into the print head to meter the flow of ink thereto. The valve arrangement uses a piezoelectric activated beam which opens and closes the gate valve comprising a plug secured to the beam, a diaphragm and a seal along with a valve seat through which passes a valve orifice.